Electrical consumers with high power ratings, for example, electric motors in electric drive systems for industrial production technology are not usually connected with their terminals directly to a power network, but are connected thereto via an electric circuit breaker. Therefore, for example, the aforementioned electric motors are connected to a 380V three-phase power network as circuit breakers known as “contactors”. Thus, for rapid and reliable complete separation of the consumption from the power network, the circuit breaker is opened.
The circuit breaker is usually operated with a control voltage of 24V, that is, it is closed, to connect the electrical consumer to the network, by applying the control voltage of 24V. For various reasons, for example, safety considerations, a circuit breaker of this type has an interrupter, for example, in the form of an emergency-stop switch or a limit switch. In the event of an emergency or a fault with the load, the interrupter is activated, interrupting the control voltage to the circuit breaker, so that the circuit breaker opens and thus reliably disconnects the electrical consumer from the power network. The circuit breaker and the interrupter together comprise an electrical protection system for the electrical consumer.
A number of solutions are currently available for protection systems. It is known, for example, to connect circuit breaking electronics having digital inputs to which the interrupter is connected, on the line side of the circuit breaker. Herein, the interrupter does not actually interrupt the control voltage of the circuit breaker, but merely triggers a signal for the circuit breaking electronics, which then performs this task. A design of this type has the disadvantage, for example, that in the event of an error in the circuit breaking electronics, even with the interrupter triggered, the circuit breaker does not open.
In other variants of protection systems, therefore, the interrupter is connected as the first element to the supply lead for the control voltage. By triggering the interrupter, the circuit breaker is reliably disconnected from the control voltage and it opens. By this means, however, all the other components, for example a plant control system, that are also supplied by the control voltage, are likewise rendered power-free. Therefore, following renewed closing of the interrupter, the whole system including the plant control system must be restarted, which can result in equipment having a very long recovery time. The power-free plant control system is therefore unable to perform any other functions during the equipment idle time, but is switched off entirely.
An arrangement of this type involves a high level of wiring effort, since a relatively large plant may, for example, have a plurality of interrupters distributed throughout it and the control voltage must be fed right through the plant via all the interrupters in series until it reaches the plant control system itself or the individual circuit breaker.